Farmers no longer just have to worry about whether it will rain too much or too little, or whether prices for their crops will be high enough to cover their costs. Now, growers increasingly are on edge about big data.

They’re concerned about the privacy of the remarkably precise data that’s now being collected about every aspect of how they farm. That includes what types of seeds they plant and where; how much and what kinds of chemicals they’re applying to their crops and where; and the exact crop yields at any single point in their fields.

All that data is computerized and marked via GPS to the exact point on the farm where it’s found.

What if a company could make a killing on the commodity markets because it had access to the real-time data on the quantity and quality of the corn that farmers were combining on a fall day in the Midwest? “That data has real value to it,” said Brian Marshall, a Missouri farmer. Last year, farmers harvested more than $60 billion in corn, so even tiny swings in markets can add up.

What if an environmental group could use a lawsuit to find out exactly how much of a pesticide farmers had applied to their fields?

And what if a seed company started boosting its prices for one farmer but not for a neighboring grower, because the firm knew the first farmer produced bigger crops than the other?

“Precision farming technology is really exciting and presents a lot of opportunities for agriculture ... but data and privacy issues are very important,” said Scott VanderWal, a grower who is president of the South Dakota Farm Bureau.

The data’s exact nature has allowed farmers to increase their crop yields for several years, even in the face of droughts and flooding, while using fewer chemicals.

Until now, the information has been safely stored in the farmers’ computerized tractors and combines or their home computers. But the biggest names in agribusiness, including DuPont Co., Dow Chemical Co. and Deere & Co., as well as Monsanto Co., are taking the technology to a new level of sophistication and usefulness by collecting and analyzing it for farmers online and via the cloud.

The concerns were heightened last fall, when Monsanto announced it was spending almost $1 billion to acquire the Climate Corp., a company founded by ex-Google engineers that compiles hyperlocal weather data and uses yield forecasting and agronomic modeling to insure farmers’ profits. Farmers can access the data through the company’s website or on mobile devices.

The Climate Corp. acquisition followed Monsanto’s purchase of Precision Planting Inc., an Illinois company that makes equipment for inserting seeds at exact depths and spacing. Late last year, two Monsanto rivals in the biotech seed business, subsidiaries of DuPont and Dow, announced partnerships with John Deere that will challenge Monsanto in data analysis.

Then there are concerns about what the government might do with the data. Earlier in 2013, farm groups were outraged when they learned that the EPA had turned over to some environmental groups information about livestock farms, including the numbers of animals in production and farmers’ phone numbers. The EPA said the information was publicly available but later asked for the data back.

Leading the way in raising questions about data privacy is the American Farm Bureau Federation, the nation’s largest farm organization.

The group organized meetings last fall with a series of companies, including Monsanto, Deere, Dow and DuPont, to discuss the privacy issues. And this month, delegates to the organization’s annual meeting approved a 13-point policy laying out how farmers’ data should be handled and protected.

Among other things, the policy states that any data collected from farmers should remain their property and that companies should return data to farmers who request it. The policy says no data should be deposited with a government agency, where it could be subject to public release under the Freedom of Information Act.

“In general, our folks obviously see the value in this [technology] and they absolutely believe that the new big data is going to provide them with a way to be more efficient,” said Mary Kay Thatcher, a lobbyist for the organization.

The Farm Bureau isn’t seeking legislation to deal with the data issue, and hasn’t even decided to seek an industry-wide policy. Farmers are just beginning to learn about the implications as they began testing various technologies, Thatcher said.

Representatives of Monsanto say farmers are asked whether the company can collect the data. But the officials stopped short of saying, for example, that Monsanto would not use the information to individually set the prices it charges for biotech seed.

“It’s so early to even speculate on something like that. We would obviously vary our pricing via a number of different means,” said spokesman Lee Quarles.

As for farmers’ concerns about market speculation, Monsanto does trade in commodities markets, but only in a limited way to protect its risk as a seed producer, the company said in an emailed statement.

“Monsanto does not use financial derivative instruments for the purpose of speculating in foreign currencies, commodities or interest rates,” the company said.

A new technology called FieldScripts that Monsanto is launching in Illinois, Indiana, Iowa and Minnesota this year will direct farmers’ computerized planters to insert the best variety of corn seeds, at the optimal rate, for each part of their fields, based on yield and soil fertility data that the growers have submitted. Monsanto will later use the farmers’ harvest-time data to optimize the planting prescription for the following season.

According to the FieldScripts agreement with farmers, Monsanto will have the right to continue using the data even after a grower drops out of the program. In addition, the data will be used to develop the planting prescription and aggregated with other growers’ data to improve future products, under the agreement. A separate privacy policy says the data may be shared with Monsanto business partners but not with marketers.

Marshall, the Missourian who grows corn, soybeans and wheat north of Kansas City, is one farmer who won’t be turning over his data to Monsanto or any other company any time soon.

He uses GPS equipment to guide and record his planting and harvesting, and he later analyzes the data to determine exactly how each part of his fields performed. Pesticide applications also are GPS-guided to ensure that he sprays the amount he wants in each area.

Marshall is worried about how the information would be used, and he’s concerned that small seed companies and other suppliers could be put at a disadvantage compared to the industry giants.

His discussions with companies haven’t eased his concerns. A Deere representative assured him that the company’s “first priority is to sell equipment” but didn’t close the door to selling farmers’ data to another company, he said.

Marshall said data from his combine’s yield monitor can show how adjacent rows of Monsanto and DuPont seed performed, which would be extremely valuable for those companies to know.